An All Solution-Processed Lead Halide Perovskite-BiVO4 Tandem Architecture Delivering STH of 2.5%

We report an all solution-processed tandem water splitting device composed of a BiVO₄ photoanode and a single-junction lead halide perovskite solar cell (CH₃NH₃PbI₃). In this configuration, the surface of BiVO₄ photoanode is in contact with water for water oxidation reaction, and the lead halide perovskite solar cell is situated behind the BiVO₄ photoanode to supply additional photovoltage to drive water reduction reaction through a Pt gauze. This architecture allows efficient solar photon management, with BiVO₄ photoanode selectively harvesting high energy photons (< 500 nm) and lead halide perovskite solar cell selectively harvesting low energy photons (500 to 800 nm) in a single-pass excitation. By modifying the surface of BiVO₄ photoanode with an earth-abundant cobalt phosphate thin film, we showed that this design is capable of delivering solar to hydrogen conversion efficiency (STH) of 2.5 % under AM 1.5G illumination at neutral pH. Our results demonstrate the potential of using low-cost, single-junction lead halide perovskite solar cells to assist n-type metal oxides to carry out bias-free photocatalytic water splitting. The unique photoanode-photovoltaic design offers opportunities to explore other semiconducting materials with extended visible light absorption ability to further improve the STH.